A compactor is an hydraulically operated device which compresses waste in order to reduce the handling and disposal costs thereof. A conventional compactor uses an hydraulically movable ram for transferring the waste from a charge box into a compactor container wherein the waste is compressed. Frequently, there is sufficient waste for several charges to be placed sequentially into the charge box, with the result that the ram must reciprocate a sufficient number of times to transfer and compress all waste.
Repetitive reciprocation of an hydraulic cylinder and piston assembly is best carried out with the assistance of a sensing mechanism for determining when the piston has reached the end of the stroke in either direction. The prior art discloses the use of pressure sensors and electrical sensors for making this determination. The pressure sensor can determine when the piston has bottomed out because the pressure in the hydraulic system increases due to the inability of the piston to move. Pressure sensing is not desirable, however, because the system must first reach a preset pressure in excess of the operating pressure upon the completion of each stroke and this pressure may cause damage and/or wear, particularly over an extended use period. An electrical sensing system, on the other hand, normally utilizes a limit switch, a proximity switch or a magnetic switch. These switches open or close electrical circuits which cause the system to stop or to activate solenoid valves for directing fluid flow. Electrical switches are not normally suitable for compactors, however, because the cylinder and piston assembly is normally located in a relatively harsh environment and these switches, by nature of their operation, must be located within that environment.
Electrical timers have also been used to control automatic cylinder motion, particularly in one direction only. A timer mechanism, however, does not provide a positive indication of cylinder or piston position. Cylinder position can only be approximated with a timer by oversetting the timer in order to be almost absolutely sure that the piston has bottomed out. The timer mechanism, therefore, is not normally desirable because, once again, the piston must bottom out and because excess time is required for each completion of cycle.
From the above, it can be seen that there is a need for a device permitting the piston to bottom out in the cylinder without causing excessive pressure, wear or increased operating time. Such a system should not be subject to contamination or deterioration by the harsh compactor environment.